Hitherto, it has been known in the rubber industry that when a rubber composition containing a filler such as carbon black is produced, a rubber wet masterbatch is used to improve the composition in workability and in filler dispersibility therein. This is a substance obtained by mixing a filler and a dispersing solvent beforehand with each other at a predetermined ratio, dispersing the filler into the dispersing solvent by mechanical force, mixing the resultant filler-containing slurry solution with a rubber latex solution in a liquid phase, adding a solidifier such as an acid thereto to produce a solidified product, and then collecting and drying the product. In the case of using a rubber wet masterbatch, a rubber composition is obtained which is better in filler dispersibility therein, and rubber properties such as workability and reinforceability than in the case of using a rubber dry masterbatch obtained by mixing a filler and a rubber with each other in a solid phase. The use of such a rubber composition as a raw material makes it possible to produce, for example, a pneumatic tire decreased in rolling resistance and excellent in fatigue resistance, or some other rubber product.
In the above-mentioned rubber wet masterbatch-producing method, a manner for removing water originating from the dispersing solvent and the rubber latex solution from the filler-containing rubber solidified product obtained through the solidifying step may be a manner of subjecting the slurry to solid-liquid separation, for example, in a filtrating or centrifuging manner, and then using any mixer to knead the filler-containing rubber solidified product while the product is heated, thereby dehydrating the product. This dehydrating method allows the water content by percentage to be lower in the rubber wet masterbatch obtained by the dehydration as the heating temperature for the kneading is made higher. However, in a case where the calorie and/or mechanical energy applied at the time of the dehydration becomes large, the resultant rubber wet masterbatch undergoes the cleavage of its polymer molecular chains, and other inconveniences. Thus, a rubber composition to be finally obtained therefrom may be deteriorated in vulcanized rubber properties.
Patent Document 1 listed below describes a production method of drying and kneading a rubber wet masterbatch containing a rubber component and a filler while a biaxial extruder is used as a first kneader, and then using a second kneader, a Banbury mixer, to mix a rubbery chemical therewith, thereby producing a rubbery-chemical-containing masterbatch. However, in this production method, the biaxial extruder is used to dry and knead the filler-containing rubber solidified product to produce the rubber wet masterbatch; thus, a large mechanical energy comes to be applied to the rubber wet masterbatch so that the rubber component tends to be deteriorated. Accordingly, a vulcanized rubber to be finally obtained therefrom tends to be deteriorated in tearing resistance and high-strain-region stress property.
Patent Document 2 listed below describes a method for producing an elastomer composite material, including: performing the step of masticating a rubber solidified product obtained through a dehydrating step while a mechanical energy of at least about 0.3 MJ/kg (about 249 W/kg) is applied thereto; and performing a subsequent step of masticating the resultant additionally while a mechanical energy of about 0.9 MJ/kg (about 83 W/kg) is applied thereto. However, this production method also tends to make the mechanical energy applied to the rubber wet masterbatch large to deteriorate the rubber component. Accordingly, a vulcanized rubber to be finally obtained therefrom tends to be deteriorated in tearing resistance and high-strain-region stress property.